Product monitoring device and system

ABSTRACT

A product monitoring system including a releaseable locking device adapted to be secured to a product and actuatable between locked and unlocked positions. The locking device consists of a pair of movable members, one of which mounts a bimetallic member consisting of bimetal elements having different temperature coefficients of expansion, the bimetal elements being separated by an insulator. The locking device further includes a detent cooperatively associated with the bimetallic means to maintain the members in a locked position. The system further includes an electrifiable key for heating the bimetallic elements to effect displacement thereof relative to the detent to facilitate movement of the members to an unlocked position. Heating of the bimetallic member is accomplished by passing current through the two mutually insulated bimetallic elements in series. In a preferred form, electronic means are provided for automatically reducing the heating current to the bimetallic member and for lighting an indicator lamp when the bimetallic has been heated sufficiently to release the locking device, thereby protecting the bimetallic from overheating and informing the operator when to withdraw the locking device from the key.

United States Patent 1191 Keifer et al.

[451 Apr. 23,1974

[5.4] PRODUCT MONITORING DEVICE AND Primary Examiner-John W. CaldwellSYSTEM Assistant Examiner-Scott F. Partridge [75] Inventors: Terry A.Keifer, Pottstown; Allan L. I

Williams, Reading, both of Pa. ABSTRACT A product monitoring systemincluding a releaseable h k I L l [73] Asslgnee g ec Mate Systems lonvl1e lockmg devlce adapted to be secured to a product and actuatablebetween locked and unlocked positions. [22] Filed: Oct. 19, 1972 Thelocking device consists of a pair of movable members, one of whichmounts a bimetallic member con- [211 App]' 299058 sisting of bimetalelements having different temperature coefficients of expansion, thebimetal elements Cl G- being separated by an insulator. The lockingdevice 337/75 further includes a detent cooperatively associated with[51] Int. Cl. G08!) 13/14 the bimetallic means to maintain the membersin a [58] Fi d of Search locked position. The system further includes anelec- 0 /l l. 317/141 S, 36 TD; 33 5; trifiable key for heating thebimetallic elements to ef- 292/DIG. 66 feet displacement thereofrelative to the detent to facilitate movement of the members to anunlocked po- [56] R fer n s Cit d sition. Heating of the bimetallicmember is accom- UNITED STATES PATENTS plished by passing currentthrough the two mutually 3 718 922 2/1973 Williams et al. 340/280insulated bimetallic elements in Seriesa Preferred 3:458:772 7/1969Egart 307 141.4 x form, electronic means are Provided for aulomatically3,598,943 8/1971 Barrett.... 200/153 W reducing the heating current tothe bimetallic member 3,575,639 4/1971 Shaw 317/141 S and for lightingan indicator lamp when the bimetallic 3,657,603 4/1972 Adams 317/141 S Xhas been heated sufficiently to release the locking de- 3,533,06 10/1970Perelmanw 340/276 X vice, thereby protecting the bimetallic fromoverheata ft 5 ing and informing the operator when to withdraw the a er3,725,739 4/1973 Griffey 317/36 TD x lockmg dame from the 20 Claims, 18Drawing Figures mu "Ill .1 1/

|1| Q; 1 9 i u 23.3; 1 v I //d [7? A42 /06 /44 PATENTEUAPR 23 I914 FIG.I l.

PRODUCT MONITORING DEVICE AND SYSTEM BACKGROUND OF THE INVENTION Thepresent invention relates to product monitoring devices and morespecifically to a device selectively attachable to articles ofmerchandise having means for deterring unauthorized removal of themerchandise from, for example, store premises.

It is well known in merchandising that unauthorized removal ofmerchandise from supervised premises such as stores produces asignificant loss to merchants. The removal is usually due to intentionaltheft or inadvertence.

Systems have been proposed in the prior art for en abling detection ofunauthorized removal of products from premises by associating with theproduct some identifiable signal producing means which, when taken pasta detection station without authorization, will produce a suitablealarm; for example, small radio transmitters, magnetic devices, andpassive tuned electrical circuits have been secured in or on productsfor such purposes. In general, such known devices have severaldisadvantages or drawbacks. For example, it has been found that thesedevices are either of excessive bulk, expensive, inconvenient to attachto different types of goods, difficult to remove, and offensive to thebuying public.

There is disclosed in a copending application Ser. No. 112,355, filed onFeb. 3, 1971, now US. Pat. No. 3,718,922, entitled Product MonitoringApparatus, System and Method, a product monitoring apparatus and systemsuitable for the above purposes. This system includes an electricallyreleaseable locking device secured to a product which is releaseable byapplication thereto of an electrically powered key. The locking devicecomprises a pair of relatively moveable members actuatable between alocking position and a release position and an elongated bimetallicelement secured to one of the moveable members and which mounts alocking pin at its free end normally engageable in a keeper hole in theother moveable member. Heating of the bimetallic element causes it todeflect in a direction to withdraw the locking pin from the keeper hole.One of the members has a keyway within which the electricaily poweredkey may be inserted to supply-current to the bimetallic element. 1

Also, in the locking device of the above-cited copending application theheating current is passed through a portion of both of the mutuallycontacting metal strips of the bimetallic member in parallel, from twowires leading to a separate electrical connector. As a result, theheating of the strips is somewhat nonuniform and requires relativelyhigh currents; also, separate soldering steps must be performed toconnect the supply wires between'bimetallic member and connector.

In the specific form of system disclosed in the aboveidentifiedapplication, the operator or check-out attendant connects the lockingdevice tothe electrified key for what is judged to be a time long enoughto release the locking device. In order to make this time relativelyshort, the current supplied to the locking device by the key isrelatively high, and in some cases when it is applied for too long atime there is danger of damaging the key; on the other hand, if thecurrent is applied by the operator for too short a time the lockingdevice will not be released.

With the foregoing in mind, it is an object of the present invention toprovide a new and useful system for the detection of unauthorizedremoval of products from a predetermined location which is ofcomparatively simplified construction and includes a clip of simplifiedform readily attachable to articles of merchandise and an electrifiedkey applicable to the locking clip to unlock the device and permit itsremoval from merchandise by authorized personnel.

Another object of the present invention is to provide such a systemincorporating the locking clip and electrifiable key which isinexpensive and easy to employ, but difficult for the thief orshoplifter to defeat.

Another object is to provide a locking device for use on products whichis difficult for a thief to unlock on the premises.

Another object is to provide such a locking device which is inexpensiveand reliable in operation.

Another object is to provide a new and useful bimetallic member in whichthe heating thereof is more uniform, and can be accomplished with lowercurrents.

A further object is to provide means for preventing damage to thelocking device due to overheating caused by too long an application ofhigh current thereto.

A further object is to provide an indication to the operator of whencurrent has been applied to the locking device for a time sufficient torelease it.

BRIEF SUMMARY OF THE INVENTION In accordance with the invention, theseand other objects are achieved by the provision of a system in which alocking device is secured to each product on the premises to be madesecure against theft, and detecting stations are provided at one or morecheckpoints on the premises so that if one attempts to remove a producthaving -a locking device secured thereto past the checkpoint, an alarmindication will be given. The locking device is releasable by means ofan electrified key maintained on the premises for this purpose, such asat a sales register, which key is effective when applied to the lockingdevice to release it and permit the unchallenged removal of the productfrom the premises.

In one aspect of the invention, the locking device incorporates abimetallic element which in its normal locking position prevents removalfrom the object and which in response to the electrical current suppliedthereto from the key causing heating thereof, moves to a positionpermitting unlocking of the device and removal from the product.

More specifically, the locking device comprises a pair of pivotallyconnected members, one member mounting a bimetallic element and theother member having a detent which in the normal position of thebimetallic element locks the members in a closed position and whichdeflects upon application of current to a position out of the range of adetent to permit the members to be moved to a release position. Themoveable members are formed with a socket within which the release keyis engageable to supply current to the bimetallic element. The keyincorporates a moveable shuttle which when inserted into the lockingdevice is displaced to actuate a switch closing circuits to contacts ofthe key which engage contacts of the bimetallic element therebyeffecting flow of current through the bimetallic element. Thus thelocking device and key of the present invention are of a more simplifiedarrangement and are easily engaged with one another to effect unlockingof the locking device.

In another aspect of the invention, there is provided a bimetallicmember comprising a pair of adjacent different bimetal elementsmechanically joined to each other at least at two spaced-aparts points,an electrical interconnection between portions of the bimetal elemerits,a contact area on each of said elements for applying voltage betweenthem, and insulating means electrically insulating said elements fromeach other between said contact area and said electricalinterconnection, thereby to enable passage of current through said twoelements in series in response to said applied voltage. Preferably themutually insulated spaced-apart portions of the bimetal'elementsterminate in a connector socket to mate with a pair of correspondingconnector elements in a key for supplying the heating current to the twobimetal elements in series.

In a further aspect of the invention, means are provided forautomatically reducing the current supplied to said locking device bysaid key, after a period sufficient for the locking device to beoperated to its release condition by the applied current, and preferablyto provide an automatic indication that this time interval has passed.Preferably this is done by sensing the abrupt drop in voltage from thecurrent source caused by current through the locking device when it isfirst plugged in and, after a suitable delay, inserting an impedance inseries with the current path to reduce its intensity. This protects thelocking device from overheating, and tells the operator when it isappropriate to release the key from the locking device.

BRIEF DESCRIPTION OF FIGURES These and other objects and features of theinvention will be more readily understood from a consideration of thefollowing detailed description, taken in connection with theaccompanying drawings, in which:

FIG. 1 is a view of the locking device applied to an article ofmerchandise and the key about to be applied thereto to permit removal;

FIG. 2 is a similar view showing the locking device and key engaged;

FIG. 3 is a view of the locking device in the open position permittingrelease from the article of merchandise;

FIG. 4 is an enlarged side elevational view, the solid line positionshowing the device in a locked position and the broken line view showingthe device in an open position, the view being partly in section to showthe internal constructions of the locking device;

FIG. 5 is a plan view'partly in section of the locking device;

FIG. 6 is a sectional view taken on line 66 of FIG.

FIG. 7 is a view similar to FIG. 6 showing the locking device showingthe relative position of the parts with the locking device in the openposition;

FIG. 8 is a view taken on line 8-8 of FIG. 4;

FIG. 9 is a side elevational view partly in section of the electrifiedrelease key;

FIG. 10 is a plane view partly in section of-the key;

FIG. 11 is an end view into the socket portion of the key; 1

FIG. 12 is a view partly in section of the engaged locking device andkey;

FIG. 13 is a similar side view of the interengaged locking device andkey;

FIG. 14 is an electrical schematic showing of the key and power supplycircuit;

FIG. 15 is a fragmentary view of a modified form of locking device inaccordance with the present invention;

FIG. 16 is a sectional view taken on line 16-16 of FIG. 15;

FIG. 17 is a perspective view of a system incorporating control meansfor providing indication to an operator that a locking device isconditioned for release; and

FIG. 18 is a schematic of the electric circuit for the control means.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENT Referring now to thedrawings and particularly to FIGS. 1-3 thereof, there is illustrated alocking device generally designated by the numeral 10 adapted to besecured to articles of merchandise A and an electrifiable key 12operable to permit actuation of'the locking device to the open position(FIG. 3 to release it from the articles of merchandise A when desired.The locking device incorporates means to be described in detailhereinafter for effecting actuation of an alarm if the article with thelocking device applied thereto is removed past a detection station.

The locking device and key of the present invention are particularlyadapted for use in retail stores which typically include a main area fordisplaying articles of merchandise, and one or more checkout counterspast which each customer must travel on his way to an exit in the store.These checkout counters are usually provided with a cash register. Alsolocated at each checkout counter will bean electrifiable key 12 by meansof which store personnel may release the locking device 10 from articlesof merchandise as they are declared and paid for. At each exit there islocated a detection station for detecting unauthorized removal ofproducts and for producing an alarm indication of such unauthorizedremoval if an article of merchandise with the locking device 10 is takenpast the exit, each protected product on the premises having a lockingdevice 10 secured thereto. 7

The locking device, in the present instance, is illustrated as beingapplied to a fabric or the like and includes a pin which penetrates thegoods to hold the locking device firmly in place. As illustrated, thelocking device has a pair of pivot arms 16 and 18 which may be pivotedto the open position shown in broken lines in FIG. 4 after the device isunlocked so that it may then be removed from the product. When the armsare moved to the closed position as shown in solid lines in FIG. 4, thedevice snaps into its locked condition and can be released only byapplication of electric current thereto by the key 12. It is, of course,to be understood that the device may be applied to merchandise otherthan fabric. For example, the opening between the arms may encircle acord of an appliance or the like. Additionally, in some instances, itmay be more effective to place another element such as a wire or a chainto a portion of a product and to secure the protruding portions of theelement to each other by means of the locking device.

The locking device as mentioned above is such that its unauthorizedremoval past a detection station will sound an alarm. There are avariety of means by which this can be provided. For the purposes of thepresent description, it will be assumed that the locking device containsa magnet and that the detection station includes appropriatemagnetrometer apparatus for detecting the passage of a magnet past it.

As will be described in detail hereinafter, the requirement of a key ofa particular configuration and the reguirement of a certain electricalcurrent to release the locking device, make it difficult for a would-bethief or shoplifter to release the locking device. As will also bedescribed in detail hereinafter, the locking device is preferably makein a simple, convenient and inexpensive form, particularly as to thelocking and unlocking arrangement which, in accordance with the presentinvention, comprises a bimetallic element heated by the applied currentin order to effect unlocking of the device.

Considering now more specifically the structural arrangement and detailsof the electrically releaseable locking device 10 in accordance with thepresent invention, the device comprises male and female jaw members 16and 18 which are pivotally mounted to one another as at 22 so that thedevice may be selectively actuated between a closed or locking position[solid lines in FIG. 4] and an open or released position [broken linesin FIG. 4]. The members are preferably made of a plastic material andare of a simplified configuration so that they may be easily molded. Themale member comprises a generally rectangular sidewall 30, top andbottom walls 32 and 34 respectively projecting from the inner edge ofthe sidewalland a pair of opposed end walls 36 and 38, one of whichmounts the arm 16. The male member further includes a center partition40 dividing the interior into two elongated compartments 42 and 44. Thelower compartment 42 houses at least one conventional magnet 46 and theupper compartment 44 houses the bimetallic element 50.

The bimetallic element 50 as illustrated comprises a pair of thinelongated members 51 and 53 of different metals or alloys and havingdifferent temperature coefficients of expansion which are suitablysecured together, for example, by welding at their outer ends, and aresecured by means of a plastic button 52 to a wall portion 54 dividingthe compartment 44 into an inner chamber 44a and an outer rear socketportion 44b. A strip 55 of insulating material is interposd between themembers 51 and 53 of the bimetallic element 50, one of the members 51being offset at its terminal rear portion to define one of a pair ofspaced contacts 60 and 62 in the socket 56.

The female member comprises a generally rectangw lar sidewall 70 adaptedto overlie the open portion of the compartments 42 and 44 of the malemember in the assembled position and a top wall 72 coextensive with thesidewall 70 confronting and overlying the top wall 32 of the malemember. The sidewall 70 has an opening 71 through which a button 73 onthe center divider of the male member projects and which is adapted tobe upset to provide the means for pivotally securing the memberstogether. Note that the female member is open at its rear terminalportion to expose the socket 56 and form a portion of the sidewall ofthe socket. Additionally, the arms 16 and 18 of the male and femalemembers are shaped in such a manner to provide a generally circularopening 75 through which a portion of an article of merchandise maybesecured, for example, the chord of an electrical appliance.

Adjacent the forward end of the male member, the top wall and centerpartition are provided with aligned cutouts and 82 respectively, and atapered detent 84 is formed integrally with the sidewall of the femalemember which clears the pocket 85 formed by the cutouts to allow pivotalmovement of the members. The bimetallic element 50 in the normalunheated position extends across the pocket 85 so that when the deviceis locked, the flat shoulder 86 of the detent engages under thebimetallic element 50 to prevent opening of the device or pivotalmovement of the male and female members relative to one another. Now,when the bimetallic element 50 is heated, it is deflected to theposition shown in broken lines shown in FIG. 5 out of the range of thedetent 84, thereby permitting the male and female members to be pivotedabout the pivot 22 to an open position. Of course, once the bimetallicelement is cooled and returns to its normal position, the clip may beclosed, the detent having a tapered front face 87 which springs thebimetallic element 50 inwardly to permit closing. However, when thedetent 84 passes the position of the bimetallic element, it snaps backinto place to securely lock the members in a closed position. Meansdescribed in more detail below is provided for controlledly passing aheating current electricity through the bimetallic element toselectively control actuation thereof as described above.

The details of the release key are best illustrated in FIGS. 9-11inclusive. The key comprises an elongated hollow housing 102 which, forpurposes of ease of construction, is sectionalized in halves so that itmay be made by a molding operation from a plastic material. The housinghas a rear compartment 104 for mounting therein an on-off switch 106 anda forward compartment 110 for a pair of electrical contacts 112 and 114. In the present instance, the'specific mounting for the contacts 112and 114 includes a post member 116 formed integrally with the sidewallof the housing over which the contacts are mounted/An insulating member120 which is disposed between the contacts 112 and 114 is also mountedon the post member 116. In the present instance, the key includes amovable shuttle 122 normally biased to an outer position by means of thespring biased pin 126 of the on-off switch 106. The shuttle, asillustrated, is shaped to straddle the contacts 112 and 114 and in itsforwardmost position the front end of the shuttle lies flush with theouter terminal ends of the contacts in the manner illustrated in FIG. 9.The shuttle has a head portion 130 which engages a shoulder 132 in thehousing to limit the forward position. The shuttle also mounts a shim134 to insure proper contact with the pin 126. The shuttle 122 is formedwith a projection 139 at its forward end engageable with the offsetportion of the contacts to define a rear limit position (see FIG. 13).The forward end of the key has a generally rectangular shaped opening ofa size to accommodate the locking device in the manner illustrated inFIGS. 12 and 13. Additionally, the contacts 112 and 114 are spaced apartlaterally a distance so that when the locking device is inserted thereinand the shuttle actuated rearwardly, the contacts engage in the socketin the locking device and make engagement with the outer terminal ends60, 62 of the bimetallic element. In this position, the actuating pin126 is depressed to an on" position thereby closing the circuit toeffect heating of the bimetallic strip which, as described previously,permits the locking device to be actuated to an open position. Asillustrated in FIGS. 9 and 10, one of the contacts 112 is connectedthrough a lead 140 to one of the contact arms of the switch 106 and theother contact 114 is connected to lead 142 to the control circuit C.Lead 144 connects the other contact of switch 106 to the circuit C. I

The power control circuit C for the key as illustrated in FIG. 14includes a main power supply 160, a switch 162 connected through lead164 to one terminal of the power supply, the switch 162 being connectedto one side of the primary of a transformer 170. The center tap of thesecondary of the transformer is connected through electrical lead 142 toone of the contacts 114 of the key, and the lead 144 connects oneterminal of the on-off switch 106 to the electrical lead 180 bridgingrectifiers 182 and 184. The circuit also includes an indicator lamp 190which is energized when the switch 162 is closed.

Considering now briefly the operation of the locking device and key inaccordance with the present invention, assume that the locking device isapplied to an article of merchandise as shown in FIG. 1 and that thearticle has now been selected by a purchaser and delivered to a checkoutcounter. Personnel at the checkout counter are in the control of theelectrified keys. Assume that the switch 162 has been closed tocondition the key for releasing the locking device. Under thesecircumstances, the locking device is inserted in the manner shown inFIG. 2 into the forward end of the key. The locking device and key areactuated relative to one another to displace the shuttle 122 rearwardlyto actuate the on-off switch 106 thereby closing the circuit to thecontacts 112 and 114. In this position, the contacts 60 and 62 engagethe contacts 112 and 114 to complete the circuit to the bimetallicelement 50 and effect flow of current through the two elements 51 and53. After a predetermined short time period, this current heats thebimetallic element sufficiently to cause it to bend out of the range ofthe detent 84; the locking device may then be removed from the key andthe jaw members 16 and 18 pivoted to an open position to remove it fromthe article of merchandise. Of course, as the locking device is removedfrom the key, the shuttle is biased to a forward position by the springactuated plunger 126 thereby opening the circuit to the power for thecontacts 112 and 114.

FIGS. 15 and 16 show a modified form of locking device in accordancewith the present invention. The device is similar in overall structuraldetails and arrangement comprising male and female members 16a and 18awhich are pivotally secured as at 22a so that the members may beactuated selectively between a closed or locking position and an open orrelease position. In the present instance pivotal movement of themembers to the release position is controlled or limited by a rib 23amounted on the inner face of the rectangular sidewall 70a of the femalemember 18a. Upon pivotal movement of the members to a release positionthe rib 23a engages the lower edge of the center partition 4011 whichdivides the interior to define a lower compartment 42a for the magnet46a. In this manner the rib 23d determines the maximum open position.

While the circuit arrangement illustrated in FIG. 14 may be utilized, asdescribed above, to accomplish the purposes of the invention, if thelocking device is inserted into the key for too long a period, thebimetallic element may be overheated and in some cases damaged. On theother hand, if the locking device is inserted into the key for too briefan interval, the bimetallic element will not be heated sufficiently tounlock the locking device. There is therefore a preferred range of timefor applying current to the bimetallic member, which usually can beprovided by an operator with appropriate care and experience. However,the apparatus now to be described with particular reference to FIGS. 17and 18 prevents accidental overheating of the bimetallic element,indicates to the operator when the locking device has been unlocked andcan be removed, and also provides an indication that the locking devicehas been inserted into the key long enough to release the lockingdevice.

Referring first to FIG. 17, there is shown one suitable physical form ofautomatic release device in accordance with this feature of theinvention, which suitably is placed on the counter at a checkout stationso that the front face thereof faces the checkout attendant. A suitableAC supply line 200 terminates in a conventional three-pronged power plug202, which in use is plugged into a conventional three-terminal powerline socket in the store. The casing 204 contains the circuitry to bedescribed with reference to FIG. 18. The release key 12 is connected byline 206 to the circuitry within casing 204. On the front of the casing204 there are mounted a front-replaceable line current fuse 210, a linevoltage indicating pilot lamp 212, a key-operated line current switch214 and a timer lamp 216.

When power plug 202 is inserted into its appropriate receptacle andswitch 212 turned to its on position, the pilot lamp 212 lights to showthat the circuit is in operable condition; initially, the timer lamp 216is extinguished. When the key 12' is inserted into the previouslydescribed locking device 10, current is supplied to the bimetallicmember within locking device 10 for an appropriate length of timesufficient to operate the bimetallic without damaging it, and thecurrent is then automatically terminated by the circuitry within casing204. At the latter time, the timer lamp 216 is also automaticallyilluminated to indicate to the attendant that the locking device hasbeen unlocked, and that the key can be removed and the clip detachedfrom the article.

Referring now to FIG. 18 in which parts corresponding to those of FIG.17 are indicated by corresponding numerals, the three wires of the powercable 200 comprise the ground line 230 and the two hot" lines 232 and234. Line 232 is connected to the series combination of fuse 210, lineswitch 214, current limiting resistor 238, and one end of the primary240 of the iron core stepdown transformer 242. The opposite end ofprimary 240 is connected directly to line 234.

Pilot lamp 212 is connected directly between power line 234 and thejunction of resistor 238 and switch 214, so as to be illuminated onlywhen switch S1 is closed and fuse 210 is intact. Relay 243 is providedwith contacts 244 and 245 which, when relay 243 is activated to theswitch position shown in broken line by current through relay coil 250,short-circuit resistor 238 so that the entire line voltage is normallyapplied across the transformer primary 240. When there is no currentthrough relay coil 250, the relay returns to its normal position, shownin full line, in which it shorts together the relay contacts 252 and254, threby removing the short circuit across resistor 238 andconnecting timer lamp 216 across the transformer primary 240, causing itto become illuminated. The manner in which the circuit operates to causethis operation of relay 240 will be described hereinafter in detail.

In response to the alternating voltage at its primary, transformer 242produces across its secondary 260 a voltage which is supplied directlyto the release key 12 over lines 262 and 264, contained in cable 206 ofFIG. 17. For example, with a llO-volt AC line supply connected to leads232 and 234, the voltage across transformer secondary 260 may be about 3volts rms when the release key is not connected to the locking device.

In general, the remainder of the circuit provides the followingfunction. When switch 214 is closed, current flows through relay coil250 to produce direct connection between contacts 244 and 245. When thelocking device is then inserted into the release key 212, the resultantcurrent load, which may be of the order of 13 amperes, causes thevoltage across transformer secondary 260 to drop abruptly, for examplefrom about 3 volts to about 2 volts rms. The circuit senses theoccurrence of thisdrop in secondary voltage, provides a suitable delay(typically about 3 seconds) during which heating of the bimetallicoccurs, and then causes the current through relay coil 250 to beterminated, which operates the relay to remove the short-circuit acrossresistor 238. This inserts resistor 238, typically of 500 ohm value, inseries with the transformer primary 240, thereby greatly reducing thecurrent supplied to the bimetallic, typically from about 13 amperes toabout 4 amperes, by way of example. The latter level of current isentirely safe for the bimetallic and will not cause it to be damaged.

The functions of sensing the drop in voltage across secondary 260,providing a predetermined delay, and then deact uating the relay 250 areaccomplished as follows. The alternating voltage across secondary 260 ispassed through coupling capacitor 270 to a voltage doubling andrectifying circuit of generally conventional form consisting of dioderectifier 272 and 274 and capacitor 276; a resistor 278 is provided inparallel with capacitor 276 to permit the voltage across the lattercapacitor to drop rapidly when the transformer secondary voltage dropsabruptly in response to a load across it, due to plugging in of thelocking device. Line 280 connected to the lower end of capacitor 276 isthe reference voltage line for the remainder of the circuit.

The rectified and doubled voltage on line 282 serves as the supplyvoltage source for three semiconductor devices 284, 286 and 288, andalso serves to supply the above-mentioned abrupt drop in voltage to thebase of the silicon controlled switch 284 by way of the series circuitcomprising resistor 290, capacitor 292 and resistor 294 connected tothereference voltage line 280.

The silicon controlled switch device 284 is of a known type which isturned on by a positive pulse supplied to its base and remains in its oncondition until switched to its opposite, or off, position by a negativepulse, in which latter state it will remain until turned on again. Thuswhen the entire circuit is initially turned on by closing of the lineswitch 214, the voltage on line 282 searches positively, typically toabout 7 volts DC, and this surge acts through resistor 290 and capacitor292 to turn on device 284. Capacitor 292 is sufficiently large to passsuch relatively rapid voltage surges sufficiently to turn on device 284,but is sufficiently small in value to prevent device 284 from beingturned on by relatively slow changes in voltage due, for example, toslow changes in the AC line voltage.

Electrode 298 of device 284 is connected through adjustable resistor 300to supply line 282, and the other electrode 302 thereof is connected tothe reference voltage line 280. When device 284 is in its normal oncondition, electrode 298 thereof is held at a low positive potential.

Timing capacitor 206 is arranged with one of its terminals connecteddirectly to the reference voltage line 280 and its other terminalconnected through resistors 310 and adjustable resistor 312 to thepositive line 282. Accordingly, the upper plate of capacitor 306 tendsto charge to the supply voltage level. However, this upper plate is alsoconnected to electrode 298 of device 284 through diode rectifier 312 andresistor 314, the anode of rectifier 312 being connected directly to theupper plate of capacitor 306. The latter circuit of resistor 314 anddiode rectifier 312 thus prevents capacitor 306 from charging upappreciably above the reference voltage when device 284 is'on.

Transistor 286 is of the pnp type, having its base connected throughresistor 316 to the upper plate of timing capacitor 306, having itsemitter connected through resistor 318 to the positive supply line 282,and having its collector connected to the reference line 280 throughrelay coil 250 of relay 243. A capacitor 320 is preferably connectedbetween base and collector of transistor 286 to suppress tendenciestoward oscillation in the circuit, and a camping diode 322 isconnectedacross relay coil 250 to suppress undesired transients causedby switching of the current through relay coil 250.

Assuming again that device 284 is on, the low voltage maintained at theupper plate of timing capacitor 306 provides a base voltage fortransitor 286 causing the latter device to operate in its conducting, oron, condition. The other transistor 288 of the pnp type is connected totransistor 286 to form therewith a Darlington pair; thus the base oftransistor 288 is connected to the emitter of transistor 286, theemitter of transistor 288 is connected directly to the positive supplyline 282, and the collector of transistor 288 is connected to thecollector of transistor 286 so as to contribute to the current throughcoil 250 when the two transistors are turned on. More particularly, whentransistor 286 is on, its emitter voltage is held at a low value such asto hold transistor 288 also on, and both transistors contribute to thecurrent through the relay coil.

Accordingly, it will be seen that when the entire system is first turnedon, all of the semiconductor devices 284, 286 and 288 will be in theiron condition, and there will be current through relay coil 250 holdingit in the position for which resistor 238 is short circuited.

Now when the locking device is plugged into the release key, theresultant current through the bimetallic causes the voltage acrosstransformer secondary 260 to drop by about 1 volt rms and causes the DCvoltage on supply line 282 to drop by about 2 volts DC, in an abruptmanner. This negative surge is coupled to the base of device 284 andcauses it to change to its off state. As a result, electrode 298 ofdevice 284 assumes a voltage substantially equal to that on positivesupply line 282, typically about 5 volts, which cuts off conduction inrectifier 312 and permits timing capacitor 306 to charge throughresistors 310 and 312. The values of the latter timing capacitor andcharging resistors are so selected that, after the desired timinginterval (typically about 3 seconds), capacitor 306 is chargedsufficiently positively to turn off transistors 286 and 288 andterminate the current relay coil 250. This causes relay 243 to switch toits opposite condition in which current limiting resistor 238 is nolonger short circuited and lamp 216 is turned on. The removal of theshort circuit across resistor 238 immediately reduces the current to thebimetallic in the locking device to about one-fourth its original value,thus protecting it from damage, and the lighting of the lamp 216 informsthe operator that the locking device can be removed from the key andopen.

When the locking device is removed from the key, the termination of theload current causes the DC voltage on line 282 to surge to its originalvalue of about 7 volts in this example, which surge is coupled throughresistor 290 and capacitor 292 to the base of device 284 to turn it onagain. This in turn turns on transistors 286 and 288, produces currentthrough relay coil 250, and returns the relay contacts to their originalposition in which resistor 238 is short circuited and timing lamp 216 isextinguished, ready for another subsequent operation.

There is thereby provided a system which automatically reduces thecurrent through the bimetallic after the locking device has been pluggedinto the key for a predetermined length of time, thereby to protect itfrom overheating and possible damage, and also automatically provides anindication to the operator that the locking device has been released andshould be removed from the key for opening and removal from the article.

What is claimed is:

1. In a product monitoring system a releasable locking device adapted tobe secured to a product, said locking device including a pair ofrelatively movable members operable between locked and unlockedpositions, bimetallic means in one of said members consisting of a pairof bimetal elements having different temperature coefficients ofexpansion separated by insulating means, detent means mounted in theother of said members and cooperatively associated with said bimetallicmeans to maintain said members in a locked position; an electrifiablekey adapted to be connected to a suitable source of electrical power,means for passing an electrical heating current from said key throughsaid bimetal elements in series thereby to heat the same and effectdisplacement out of the range of said detent means to permit movement ofsaid members to an unlocked position; means for producting an electricalsignal indicative of the initiation of current flow from said key tosaid locking device upon connection of said key to said locking deviceand means responsive to said electrical signal for automaticallyreducing the current supplied to said locking device at the end of apredetermined time interval.

2. A releasable locking device adapted to be secured to a productcomprising a pair of relatively movable members, bimetallic meansmounted in one of said members comprised of at least a pair of elongatedelements having different temperature coefficients of expansion, detentmeans mounted in a fixed position in the other member and cooperativelyassociated with said bimetallic means to maintain said members in alocked position, said bimetallic means upon application of an electricalcurrent to heat the same operable to be displaced out of the range ofsaid detent means to permit movement of said members to an unlockedposition.

3. A releasable locking device as claimed in claim 2 including meanspivotally connecting said movable members and wherein said detent islocated remote from said pivotal connection.

4. A releasable locking deviceas claimed in claim 2 wherein said movablemembers encapsulate said detent and bimetallic means so that members canbe actuated from a locked to an unlocked position only by application ofelectric current to said bimetallic means.

5. A releasable locking device as claimed in claim 2 wherein theterminal ends of the elements of said bimetallic means form a pair ofspaced contacts in a socket portion formed at one end of said members.

6. A releasable locking device as claimed in claim 2 wherein saidbimetallic means are secured tosaid one member in a manner defining aflexible portion operable when disposed in one position in the path ofsaid detent to maintain said members locked and displaceable when heatedby current to a second position out of the path of said detent topermitmovement of said members to an unlocked position.

7. A releasable locking device as claimed in claim 6 wherein said detenthas a tapered portion operable when said members are in an unlockedposition and said flexible portion is in said one position to displacesaid flexible portion when said members are actuated to the lockedposition.

8. An electrifiable key for actuating a releasable locking device havingbi-metallic means controlling unlocking of the locking device comprisingan enclosed housing, at least one pair of spaced contacts in saidhousing, a shuttle movable in said housing between a forward limitposition and a rearward limit position, biasing means normally urgingsaid shuttle to said forward limit position, switch means adapted to beconnected to a suitable source of electrical power, said shuttle movablein one direction to said rearward limit position by the locking devicewhen engaged therewith to actuate said switch to close the circuit tothe electrical power source producing flow of an electrical currentthrough said contacts to the bimetallic means, said switch means beingopen when said shuttle is in said forward limit position.

9. An electrifiable key as claimed in claim 8 wherein said housing has arecess at one end into which the locking device may be .inserted toengage said shuttle.

10. An electrifiable key as claimed in claim 8 wherein said switchactuator is spring biased and normally maintains said shuttle in aforward limit position.

11. An electrit'iable key as claimed in claim 10 wherein said contactsare mountedin a fixed position and wherein said shuttle is mounted formovement relative thereto between the forward limit position wherein thecontacts are covered by said shuttle and the rearward limit positionwherein said contacts are exposed.

12. In a bimetallic device comprising a pair of adjacent bimetalelements having different temperature coefficients of expansion andmeans securing said elements to each other mechanically at least at twospaced-apart points, the improvement comprising means electricallyinterconnecting portions of said elements to each other, a contact areaon each of said elements for applying a voltage between said elements,and insulating means electrically insulating said elements from eachother between said contact areas and said electrically interconnectedportions of said elements, thereby to enable passage of current throughsaid elements in series in response to said applied voltage.

13. A bimetallic device comprising:

a pair of adjacent bimetal stips having different temperaturecoefficients of expansion;

junction means electrically and mechanically joining said stripstogether at one of their ends;

an insulating strip of material between said bimetal strips to maintainthem insulated from each other except at said one ends thereof; and

fastening means insulatedly securing said bimetal strips together at apoint spaced from said junction means, with said insulating stripbetween them.

14. A bimetallic device according to claim 13, in which the portion ofsaid bimetal strips on the side of said fastneing means opposite fromsaid junction means diverge to provide spaced-apart connector elements.

15. A bimetallic device according to claim 13, comprising a casing forsupporting said bimetallic strips, said casing surrounding saidconnector elements and providing a socket for receiving a plug to applya voltage between said connector elements.

16. In a system comprising a locking device adapted to be attached toarticles and releasable therefrom in response to a predeterminedmagnitude of electrical current supplied thereto from an electrified keyfor a predetermined time interval, said locking device being subject todamage in the event said current is supplied thereto for a time intervalsubstantially longer than said predetermined time interval, theimprovement comprising:

means for producing an electrical signal indicative of the initiation ofcurrent flow from said key to said locking device upon connection ofsaid key to said locking device; and

means responsive to said electrical signal for automatically reducingthe current supplied to said locking device at the end of saidpredetermined time interval.

17. In the system of claim 16, indicator means and means forautomatically actuating said indicator means at the end of saidpredetermined time interval.

18. A system in accordance with claim 16, comprising a source of saidcurrent, and in which said means for producing said electrical signalsaid initiation of current flow comprises means for producing an abruptdecrease in the voltage of said source in response to said initiation ofcurrent flow; means for connecting an impedance in series with thecurrent path from said source to said key in response to said decreasein voltage thereby to reduce said current; and means for delaying saidreduction of said current with respect to the time of said decrease involtage by an amount substantially equal to said predetermined timeinterval.

19. A system in accordance with claim 18, in which said means forconnecting an impedance in series comprises relay means having a firstposition in which said impedance means is in series with said currentpath and having a second position in which it is not, and in which saiddelaying means comprises timing capacitor means and a control circuittherefor responsive to said decrease in voltage to initiate charging ofsaid capacitor means, said control circuit being responsive to increasesin said voltage to discharge said capacitor means.

20. A system in accordance with claim 19, comprising indicator lampmeans, and means for illuminating said lamp means only when said relaymeans is in said first position.

1. In a product monitoring system a releasable locking device adapted tobe secured to a product, said locking device including a pair ofrelatively movable members operable between locked and unlockedpositions, bimetallic means in one of said members consisting of a pairof bimetal elements having different temperature coefficients ofexpansion separated by insulating means, detent means mounted in theother of said members and cooperatively associated with said bimetallicmeans to maintain said members in a locked position; an electrifiablekey adapted to be connected to a suitable source of electrical power,means for passing an electrical heating current from said key throughsaid bimetal elements in series thereby to heat the same and effectdisplacement out of the range of said detent means to permit movement ofsaid members to an unlocked position; means for producting an electricalsignal indicative of the initiation of current flow from said key tosaid locking device upon connection of said key to said locking deviceand means responsive to said electrical signal for automaticallyreducing the current supplied to said locking device at the end of apredetermined time interval.
 2. A releasable locking device adapted tobe secured to a product comprising a pair of relatively movable members,bimetallic means mounted in one of said members comprised of at least apair of elongated elements having different temperature coefficients ofexpansion, detent means mounted in a fixed position in the other memberand cooperatively associated with said bimetallic means to maintain saidmembers in a locked positioN, said bimetallic means upon application ofan electrical current to heat the same operable to be displaced out ofthe range of said detent means to permit movement of said members to anunlocked position.
 3. A releasable locking device as claimed in claim 2including means pivotally connecting said movable members and whereinsaid detent is located remote from said pivotal connection.
 4. Areleasable locking device as claimed in claim 2 wherein said movablemembers encapsulate said detent and bimetallic means so that members canbe actuated from a locked to an unlocked position only by application ofelectric current to said bimetallic means.
 5. A releasable lockingdevice as claimed in claim 2 wherein the terminal ends of the elementsof said bimetallic means form a pair of spaced contacts in a socketportion formed at one end of said members.
 6. A releasable lockingdevice as claimed in claim 2 wherein said bimetallic means are securedto said one member in a manner defining a flexible portion operable whendisposed in one position in the path of said detent to maintain saidmembers locked and displaceable when heated by current to a secondposition out of the path of said detent to permit movement of saidmembers to an unlocked position.
 7. A releasable locking device asclaimed in claim 6 wherein said detent has a tapered portion operablewhen said members are in an unlocked position and said flexible portionis in said one position to displace said flexible portion when saidmembers are actuated to the locked position.
 8. An electrifiable key foractuating a releasable locking device having bi-metallic meanscontrolling unlocking of the locking device comprising an enclosedhousing, at least one pair of spaced contacts in said housing, a shuttlemovable in said housing between a forward limit position and a rearwardlimit position, biasing means normally urging said shuttle to saidforward limit position, switch means adapted to be connected to asuitable source of electrical power, said shuttle movable in onedirection to said rearward limit position by the locking device whenengaged therewith to actuate said switch to close the circuit to theelectrical power source producing flow of an electrical current throughsaid contacts to the bimetallic means, said switch means being open whensaid shuttle is in said forward limit position.
 9. An electrifiable keyas claimed in claim 8 wherein said housing has a recess at one end intowhich the locking device may be inserted to engage said shuttle.
 10. Anelectrifiable key as claimed in claim 8 wherein said switch actuator isspring biased and normally maintains said shuttle in a forward limitposition.
 11. An electrifiable key as claimed in claim 10 wherein saidcontacts are mounted in a fixed position and wherein said shuttle ismounted for movement relative thereto between the forward limit positionwherein the contacts are covered by said shuttle and the rearward limitposition wherein said contacts are exposed.
 12. In a bimetallic devicecomprising a pair of adjacent bimetal elements having differenttemperature coefficients of expansion and means securing said elementsto each other mechanically at least at two spaced-apart points, theimprovement comprising means electrically interconnecting portions ofsaid elements to each other, a contact area on each of said elements forapplying a voltage between said elements, and insulating meanselectrically insulating said elements from each other between saidcontact areas and said electrically interconnected portions of saidelements, thereby to enable passage of current through said elements inseries in response to said applied voltage.
 13. A bimetallic devicecomprising: a pair of adjacent bimetal stips having differenttemperature coefficients of expansion; junction means electrically andmechanically joining said strips together at one of their ends; aninsulating strip of material between said bimetal strips to maintainthem insulated from each other except at said one ends thereof; andfastening means insulatedly securing said bimetal strips together at apoint spaced from said junction means, with said insulating stripbetween them.
 14. A bimetallic device according to claim 13, in whichthe portion of said bimetal strips on the side of said fastneing meansopposite from said junction means diverge to provide spaced-apartconnector elements.
 15. A bimetallic device according to claim 13,comprising a casing for supporting said bimetallic strips, said casingsurrounding said connector elements and providing a socket for receivinga plug to apply a voltage between said connector elements.
 16. In asystem comprising a locking device adapted to be attached to articlesand releasable therefrom in response to a predetermined magnitude ofelectrical current supplied thereto from an electrified key for apredetermined time interval, said locking device being subject to damagein the event said current is supplied thereto for a time intervalsubstantially longer than said predetermined time interval, theimprovement comprising: means for producing an electrical signalindicative of the initiation of current flow from said key to saidlocking device upon connection of said key to said locking device; andmeans responsive to said electrical signal for automatically reducingthe current supplied to said locking device at the end of saidpredetermined time interval.
 17. In the system of claim 16, indicatormeans and means for automatically actuating said indicator means at theend of said predetermined time interval.
 18. A system in accordance withclaim 16, comprising a source of said current, and in which said meansfor producing said electrical signal said initiation of current flowcomprises means for producing an abrupt decrease in the voltage of saidsource in response to said initiation of current flow; means forconnecting an impedance in series with the current path from said sourceto said key in response to said decrease in voltage thereby to reducesaid current; and means for delaying said reduction of said current withrespect to the time of said decrease in voltage by an amountsubstantially equal to said predetermined time interval.
 19. A system inaccordance with claim 18, in which said means for connecting animpedance in series comprises relay means having a first position inwhich said impedance means is in series with said current path andhaving a second position in which it is not, and in which said delayingmeans comprises timing capacitor means and a control circuit thereforresponsive to said decrease in voltage to initiate charging of saidcapacitor means, said control circuit being responsive to increases insaid voltage to discharge said capacitor means.
 20. A system inaccordance with claim 19, comprising indicator lamp means, and means forilluminating said lamp means only when said relay means is in said firstposition.